The present invention relates to an optical modulator using an electrically controllable diffraction grating.
A prior diffraction grating has a glass substrate with a high density of thin, parallel lines on the surface of the same, and is mainly used in the academic spectral analysis field. The characteristics of this diffraction grating are rigidly defined by the size and the period of said lines, and the wavelength of a light beam applied to the diffraction grating, and the characteristics cannot be changed after the diffraction grating is manufactured. Accordingly, the prior diffraction grating has the disadvantage in that its field of use is very limited.
Controllable diffraction gratings which overcome the above diadvantages are shown in (1) "Low Voltage Optical Modulator Using Electro-optically Induced Phase Grating" by T. Motoki, in "Applied Optics", vol. 12, No. 7, 1973, pp 1472 published in U.S.A., and (2) "Nano-second Base-band Optical Diffraction Modulator" by M. G. F. Willson etc. in "Electronics Letters" vol. 7, No. 10, 1971, pp 267 published in England. These prior art gratings are partially controllable, but they have the disadvantage that the substrate on which they are formed must be optically transparent and consequently, the selection of material for the substrate is very limited.